Campaigners from the Society for the Protection of the Unborn Child outside Westminster. Photograph: Stefan Rousseau/PA

Rawnie Chapman-Kitchin, 15, was aghast when her teacher compared abortion to Nazism, saying that in time history would view both with the same revulsion. "I'd been expecting a regular RE class, but a different teacher was called in to do a talk called Abortion is Murder," she says. "He showed horrifying pictures of dead foetuses, but there was no opportunity to opt out. It was very much a case of 'this is the way you need to think'.

"One person put their hand up at the end and said, 'You've changed my mind. I thought abortion was OK, but now I don't.' Others agreed and still hold those views. But I've since found out that some of what the teacher was saying isn't even true - for example, about how they do abortions."

Anti-abortion presentations in schools are not a one-off. At the beginning of this term, the Society for the Protection of the Unborn Child (Spuc) wrote to every secondary school in the country to offer its PowerPoint presentation. Katherine Hampton, education officer at Spuc, says she visits around 10 schools a term and supervises a further 40 trained speakers across the country. The organisation Life delivered 816 school talks during 2006-07 through its "active schools department", reaching 37,803 students across 316 schools - a 20% increase on the previous year. Then there are the individual teachers, like Rawnie's, who offer to air their anti-choice views to classes. Having realised that teenagers are the most susceptible to anti-abortion messages, lobbyists are increasingly targeting 13- to 17-year-olds.

While each has differing tactics (for instance, Life doesn't use images), what they all share is an approach to abortion that is highly subjective. What's more, they stand accused of presenting information that is at best questionable and at worst incorrect. Spuc, for example, tells teenagers there are links between abortion and breast cancer, although organisations such as Cancer Research UK and Breakthrough Breast Cancer have consistently presented research to prove there is no link. The Royal College of Obstetricians and Gynaecologists (RCOG) categorically states that abortion is not associated with an increase in breast-cancer risk. Life says it tells pupils that, although abortion is becoming safer, there are studies that have shown an increased risk of infertility. The RCOG states that there are no proven associations.

Why do schools allow these speakers in? Three reasons. First, they feel they ought to cover abortion but, given its contentious nature, are anxious about how to approach it. An offer from a so-called specialist organisation can come as something of a relief. Second, abortion usually sits within RE, where it is covered as a moral issue, so teachers often welcome the idea of visiting speakers with a strong view. Third, schools like outside speakers - it shows they are widening their pool of educators.

The anti-choice lobby has reason to celebrate. A recent YouGov poll found that only 29% of 17-year-olds were strongly pro-choice. The remainder are either negative or ambivalent, and although it was a small survey, most people in the field agree the figure sounds about right. The UK Life League - the most hardcore of all the anti-abortion groups - claims it has never had so much support from teenage girls. "We've noticed a massive difference in the last three years alone. Whereas they used to be largely unreceptive, they now tell us how pleased they are about the work we're doing. I'm not sure what's different, but I wish I could have bottled it up 30 years ago," says Jim Dowson, its national coordinator.

Samantha Bracey, Rawnie's mother, is amazed that more parents, and schools, are not taking a stand. "I was really concerned when my daughter told me about the disturbing images she was shown, and even more so when I discovered she'd been told abortions were carried out via caesarean section [called hysterotomy abortions], which isn't true. The teacher consistently referred to the embryo or foetus - medically recognised terms - as a baby, and claimed that pro-abortionists did not use the term 'baby' as it was too emotive."

When Bracey approached the school - Chapel-en-le-Frith high school in Derbyshire - she was assured that, in future, pro-choice opinions would be explored within the class. "But the teacher who gave the talk still said his intention would be to win his argument, which seems to me to be missing the purpose of education," she says. "Surely issues like abortion should be addressed in a way that makes all the facts available, rather than merely opinion, thus enabling the students to reach a conclusion by informed debate. When it comes to abortion, it's so important - it can affect the rest of their lives."

Stating the facts

Only one organisation, Education For Choice (EfC), gives pro-choice talks in schools, but with a fraction of the funding and staffing that Spuc and Life enjoy, the number of pupils it reaches is minimal. Lisa Hallgarten, EfC's head of policy and communications, says: "We don't go in and say you should always have an abortion under every circumstance, which would be the opposite of what they say. We say, here are the facts and it's absolutely your decision." If someone comes into the classroom believing abortion is murder and leaves still believing that, Hallgarten does not consider it failure. "That's not our mission. But if someone walks in believing that abortion makes you infertile and they leave with that view, then that would be failure."

What's needed, she believes, is for schools to move away from presenting the issue as a dichotomy: abortion - is it right or wrong? "That's so often how it's addressed in schools, which completely ignores the sexual health aspect. Far more productive is exploring how women get into the situation where they consider abortion. Could they have avoided the unwanted pregnancy? And are there situations where it is unavoidable - for example, where contraception fails? Then you can move on to talk about people's different values, at which point we explore some of the reasons people are against abortion as well as reasons why others find it acceptable."

Like many teachers, Stuart Ash, headteacher at Chapel-en-le-Frith high school, had never heard of EfC. "We would like nothing more than to present objective, balanced information to our young people. But we found it hard to find any such resource material available for schools and appropriate for the GSCE age range," he says. "People say, 'Why not look on the internet?' There's certainly plenty of material there, but you don't know who's behind it. That's why we offered a lesson with the 'against' argument and a few weeks later the other side of the coin - although, with hindsight, we feel that time permitting, it would be better to explore both sets of views within the same lesson." He adds that the lesson attended by Rawnie was prefaced with a statement that the teacher's standpoint was only one of a range of views.

Hallgarten says it is the misinformation presented to pupils that most infuriates her, in particular what she calls the "huge propaganda machine" around post-abortion trauma. "There is no evidence that abortion per se causes trauma, yet it has been the most effective propaganda tool that has helped much of the anti-abortion movement move from a blame culture (how can you murder your baby?) to women as victims (you poor thing, you'll be terribly traumatised if you have one)."

Many anti-abortion organisations refer to "post-abortion syndrome", whose symptoms can include panic attacks, relationship problems, self-harm, drug and alcohol abuse, and depression. In fact, it is not a recognised medical condition. In August, the American Psychological Association concluded: "There is no credible evidence that single elective abortion of an unwanted pregnancy in and of itself causes mental-health problems for adult women."

When it comes to imagery, anti-abortion organisations appear to have two tactics. "Some organisations use compelling images of happy-looking faces in the womb, which are without doubt beautiful," says Hallgarten. "But many claims are made that they are doing things, like smiling, that in fact they can't do until after they are born. Another tactic used in schools is to show a photograph of a foetus at, say, 24 weeks, and then talk about an abortion at 12 weeks. It's all about implication. Then there's the purported pictures of foetal parts in buckets, which is obviously distressing and can have a big impact."

Spuc opts for both types of pictures. Having watched its presentation, labelled "standard abortion talk 2008", I am not surprised to hear that in one class of 16- and 17-year-olds shown the presentation in July, half the students left distressed and some were physically sick.

"The presentation I am going to show you today will give you the information about abortion that we believe everyone should know," it starts. "You will see seven pictures showing the development of the baby and four pictures showing the different methods of abortion. The abortion pictures are not very pleasant to look at, and I will warn you before I show them. My intention is not to shock you, rather to inform you sensitively of the truth and reality of what abortion entails."

I was shocked. Having built up a sentimental picture of the first weeks of foetal development, the first of the abortion images is brutal and bloody, showing a foetus being pulled by its legs out of a woman's cut-open stomach. The method claims to be a hysterotomy abortion - one that is so rarely employed (and only ever used when no other method is safe for the woman) that statistics are not collected on it in the UK. In the US, it is estimated at less than a tenth of 1% of abortions. Spuc says that while some speakers have dropped this image from their talk, others have not.

Another picture shows a premature baby called Kelly and is accompanied by the statement that: "As long ago as 1985, a study by RCOG said that 72% of babies born between 20 and 25 weeks survived, yet the laws in our country allow unborn babies the same age as Kelly to be aborted." Spuc says it tells teenagers that the figure is probably far higher today. The actual figures from the 2000 EPICure study into the survival of extremely premature infants, which the RCOG cites and is the best source of information on this topic, says 33% of babies born at 24 weeks, 19.9% at 23 weeks, and 9.1% at 22 weeks live long enough to be discharged from hospital.

Hampton believes that, among young women, the tide is turning towards anti-abortion and likes to think that Spuc has been influential. But she insists its intention is simply "to leave people with factual information that they can think about", and adds that images are only used with the permission of the teacher, which is given in about 50% of cases.

Samantha Crozier, an RE teacher, was one who gave permission. "I told Spuc the talk would be to 16-year-olds and that I didn't want them to show anything too graphic, and they said that was fine. Yet the images the presenter used were so shocking that one teacher walked out and another felt she had to turn her back to the class. Many of the students also turned away, while a few left the room and a couple even went home because they were so upset. We had to bring all the students who remained together afterwards and apologise. As far as I'm concerned, it wasn't a case of those pictures not being appropriate for that age group - they're not appropriate for any age group. There was a question of things being outdated, too. One of the images they used was from 1978 and some of the procedures they talked about aren't even used today."

Life has a different approach, says its education officer, Michaela Aston. "We want young people to think for themselves. We're not going to tell them what to think. Of course, it would be lovely if they're pro-life, but if they're not that's fine."

Logical position?

Life's main bugbear appears to be that most people assume abortion is "perfectly fine" because it's legal. "That's the general perception. But really we don't want kids to inherit these views. We want them to think about the principles they live by, what values are important to them. We never show any horrid pictures, ever, as a matter of policy. And we look at all the arguments for and against so that they engage with the debate," says Aston. It sounds reasonably unbiased, but Aston believes - as every member of Life does - "that because we believe human life begins at the moment of fertilisation, then the pro-life position is the only logical position to take".

Although not explicitly an anti-abortion organisation, Care Confidential is another piece in the jigsaw. Claiming to offer a neutral service, "which helps teenagers think through what options are available to them and how they might feel about those options when faced with a crisis", the charity provides talks in schools. A bit of digging turns up some significant issues. First, Care Confidential is run by the charity Christian Action Research and Education (Care), whose charitable aims, as listed with the Charity Commission, are: "The advancement and propagation of the Christian Gospel and in particular Christian teachings as it bears on or affects national and individual morality and ethics." Second, the vast majority of stories from women who have had abortions that it publicises are negative, although it does publish all the stories it receives. And finally, despite research pointing to the significant and lasting psychological damage that can be faced by women who put their babies up for adoption, Care Confidential encourages young women to consider adoption as a positive alternative. Care Confidential declined to make any comment for this article.

Religious bias

Dr Geraldine Brady, research fellow at Coventry University, says she has come across organisations that play down their anti-abortion agenda by presenting themselves as neutral. "One of them [not Care Confidential] was Christian-based, employing professionally trained counsellors. However, it transpired that the religion did seep through, and some of the literature they were providing to schools revealed that quite clearly. They were going into schools to educate young people about the facts around termination, foetal development, abortion procedures, but with the literature that was used and the way it was used, it became obvious that an anti-abortion stance was coming through."

Research shows that even where pro-choice groups have been invited into schools to "balance" the picture, it can be too late. "We found people from pro-choice groups in this situation felt they were up against it, having been cast in a negative light," says Brady.

Ann Furedi, chief executive of the British Pregnancy Advisory Service, believes we should all be concerned about anti-choice organisations accessing young people. "From their point of view, targeting these particularly impressionable and idealistic people is seen as a tactic. They are well resourced, sometimes drawing on funding from the US, and they have a real mission." As a result, she says, and despite the increase in the numbers of young people having abortions, "there is a growing sense among them that it's ultimately wrong".

Nobody I spoke to suggested that anti-abortion views should be shielded from young people. But, says Furedi, any discussion in school must be honest and provide accurate, impartial and up-to-date information. "Better still," she says, "let's move it out of the RE room and be much more upfront about the fact that one in three women will have an abortion at some time in their lives and that basically, if you're fertile and sexually active, you are at risk of an unwanted pregnancy."